I became a science writer — well, at least a part-time one — because I lived through SARS. I was a reporter for TIME’s Hong Kong office 10 years ago, mostly covering books, films and whichever exotic destination I could convince my editors to send me to. (Like … Guangzhou!) But when SARS started spreading in Hong Kong in the spring of 2003 — from where it leapt to much of the rest of the world — I was hooked immediately. Experiencing science in real time, with human lives and billions of dollars on the line, was pure cut excitement. I remember getting a glimpse through an electron microscope of the coronavirus that caused SARS, not long after researchers at Hong Kong University had identified it, and being fascinated that a packet of genes, just 100 nanometers in diameter, could cause so much trouble. (For the best book on the SARS outbreak, check out former TIME Asia editor Karl Greenfeld’s China Syndrome — and not just because I’m in the index.)

But my conversion wasn’t just about the rush of following an outbreak in real time. An emerging infectious disease like SARS pulls back the curtain on our world and demonstrates just how interconnected we all are, in more ways than just the global economy or international air travel. SARS, like most new diseases, started in an animal before jumping across the species barrier to human beings. The original reservoir for SARS was actually a bat, and it’s still not clear how the virus managed to cross from them to us, though the anything-goes standards of the live markets of southern China, where wild animals of all sorts are available for consumption and where the SARS outbreak began, definitely played a role. Researchers initially thought that civet cats transmitted the virus to human beings — Chinese officials even culled thousands of civet cats in the months after SARS to prevent a resurgence — though now it seems possible that the cats caught it from us. No matter how the virus jumped, it made one thing clear: virologically speaking, we’re connected not just to humans, but to many other species. Their health is ours.

That’s worth keeping in mind as health officials grapple with another new coronavirus. Since the new pathogen first came to light in Saudi Arabia last fall, at least 15 people have been infected and more than half have died. Like SARS, it causes severe respiratory illness — and like SARS, there’s no ideal treatment. So far the new coronavirus hasn’t been able to spread easily among human beings, and it’s possible that — like the vast majority of emerging pathogens, including SARS itself — it will never fully establish itself in our species. But as the virologist Ron Fouchier of Erasmus University in the Netherlands told the Guardian’s Ian Semple:

We don’t know whether this virus has the capability to trigger a full epidemic. We are completely in the dark about it. We think what we are seeing is just the tip of the iceberg, but we don’t know how big the iceberg is, or where the iceberg is.

What Fouchier is saying is true for emerging pathogens more generally. Animal health gets just a fraction of the resources that human health does, which is why we are rarely able to detect new viruses before it’s too late and they’ve already crossed the species barrier. In the wake of SARS and the avian flu flare-ups over the past decade, however, that is beginning to change. I’ve written before about the virologist Nathan Wolfe and his Global Viral Forecasting group, which tries to use on-the-ground surveillance and computer modeling to predict when and where new viruses will emerge to threaten the human race. But there other groups working to police the boundaries between human and animal health, and one of them — the New York City–based EcoHealth Alliance — has a new paper out that demonstrates just how many unknown coronaviruses are out there, competing to be the next SARS. “This is really critical stuff,” says Peter Daszak, the president of EcoHealth. “It was on the back burner, but with SARS and everything after, it’s become a major concern.”

Researchers from the group screened more than 600 bats from 42 species in Mexico, looking for new viruses. (Bats, for reasons that aren’t clear, seem to play a critical role in spreading new viruses to humans; besides SARS, bats were also the reservoir for the Nipah virus, which causes a neurological and respiratory disease that’s infected hundreds of people, chiefly in Southeast Asia.) The investigators were able to identify 13 distinct coronaviruses, and all but one had never been characterized before. As viral-fishing expeditions go, this was very, very good — and very, very scary; the fact that there are that many new viruses in a relatively small sample of bats is a sign of just how little we know about the microbial threats on the horizon. “If you start looking around, you’d find hundreds of thousands of unknown viruses waiting to be discovered,” says Daszak. “Most will be harmless — but some will be lethal.”

Daszak notes that the Saudi coronavirus seems unlikely to be anything more than an isolated threat. But as more and more people crowd the planet — and as we push back forests and other wildlife habitats, putting us in ever closer contact with a range of new and potentially germ-filled species — the danger from emerging diseases is only likely to grow. “You have five new diseases emerging each year, and that rate is increasing,” says Daszak. “We have to be able to increase our surveillance.” The truth is that as bad as SARS was — the disease killed nearly 1,000 people and cost tens of billions of dollars worth of damage — we were lucky that the outbreak was as mild as it was, just as we were lucky with the relatively weak influenza pandemic of 2009 (which, don’t forget, initially spread to human beings from pigs). It’s unlikely we’ll be so lucky every time.